The Russians have come within “hand-grenade range” of American troops in Syria — sparking fears of friendly fire and increased tensions, a report says.

“Escalation is bound to happen,” explained Andreas Krieg, a professor at the Defense Studies Department at King’s College London.

Speaking to NBC News, he warned that due to their close proximity, the two nations — which are now working together in the region with Kurdish YPG fighters to combat ISIS — could wind up inadvertently firing upon one another.

“These surrogates are doing their own operations and then the sponsors are doing air cover and artillery cover,” Krieg said.

US commanders first revealed how the forces were bordering one another while speaking to reporters earlier this month, according to NBC.

“[Russian and American soldiers] have converged literally within hand-grenade range of one another,” said Army Lt. Gen. Steven Townsend, commander of Combined Joint Task Force Operation Inherent Resolve.

While an estimated 1,000 American troops were believed to be stationed in Syria last month, that number may in fact be larger now that President Trump has sent several hundred more there in recent weeks, NBC reports.

“Fighting ISIS and fighting the jihadis is absolutely the first priority of the [Donald] Trump administration,” Krieg said. “This is why [Defense Secretary James] Mattis is going so hardcore after ISIS. And almost everything goes as long as they are fighting jihadis at the same time.”

Russia is believed to have 1,600 to 4,500 soldiers in Syria, NBC reports.

Before teaming up with the Kurdish fighters, the US and Russians were each on opposite sides of the Syrian civil war — with the Americans backing the rebels and the Kremlin supporting President Bashar al-Assad.

According to US Central Command, their military commanders are now in contact with each other and working together to avoid accidental casualties.

The Kremlin ultimately wants “an alliance between Russia and the United States in fighting terrorism, and to be recognized as an equal partner with the United States,” Igor Sutyagin, a senior research fellow at London’s Royal United Services Institute, told NBC.